A grass mower for collecting cut grass may be equipped with a collector, such as a bag or a box, in which the cut grass is gathered. Attachment of such a collector onto the mower can be cumbersome in that proper connection of a discharge portion of the mower with an inlet opening of the bag is not always easily established and problems such as leakage can be difficult to detect or notice. Thus, there is a need to prevent problems such as leakage in the attachment of the collector and to indicate proper connection of the collector with the mower.